From a girl's point of view: this happens to me a lot - guy comes up, tries to initiate conversation and I just ignore and don't make eye contact until they start talking to me.

Typical conversation would be like this: Guy: You don't seem very impressed. Me: I'm never impressed.

Basically I try to be as awkward and unapproachable as possible, because I want to be left alone but don't want to leave my spot. Do you guys usually flee the scene or keep at it?